You left out the fact that the anonymity of the internet can often cause people to act in ways that they would never think of doing when speaking with someone face to face.
In all three cases, though, it's the rights of the owner of the forum, and the duty of the moderators, to weigh all conversations/conflicts against the agreed upon rules of conduct and act accordingly.
If no one can, or will, enforce those protocols, a forum will break down into chaos.
There are forums on the internet that allow, or even encourage, that type of psychotic "conversation." To my understanding, THR was never intended to be that kind of place. APS has somewhat looser limitations, but those who post here are still held to certain rules of conduct. Yes, we have all, at one point or another, broken those rules of conduct, but it is not an on-going activity.
As far as I can remember, those few people who have been banned here looked at conflict as an on-going activity, specifically Masterpiece Arms, Blackburn, and Lifer come to mind.
We all have our moments that are less civil than others. The differentiation, though, is the nature of an individual's posts over time. Yes, someone can be dropped for one huge atomic bomb type comment, but most times it's an on-going pattern of conduct.